Since energy issues and global environmental issues are becoming more serious, solar cells are receiving more attention as an alternative energy for replacing fossil fuels. In the solar cell, carriers (electrons and holes) generated by light irradiation on a photoelectric conversion section composed of a semiconductor junction or the like are extracted to an external circuit to generate electricity.
A collecting electrode is provided on the photoelectric conversion section of the solar cell for efficiently extracting carriers generated at the photoelectric conversion section to the external circuit. For example, in a crystalline silicon-based solar cell using a single-crystalline silicon substrate or a polycrystalline silicon substrate, a collecting electrode made of fine metal is provided on a light-receiving surface. Also, in a heterojunction solar cell having amorphous silicon layers and transparent electrode layers on a crystalline silicon substrate, collecting electrode(s) are provided on the transparent electrode layer(s).
The collecting electrode of the solar cell is generally formed by pattern-printing a silver paste by a screen printing method. On the other hand, a method of forming a collecting electrode by a plating method has also been developed. For example, Patent Document 1 discloses a method in which an insulating layer is formed on a first collecting electrode including a low-melting-point material, the low-melting-point material is thermally fluidized to form an opening section in the insulating layer by heat annealing, and then a second collecting electrode is formed through the opening by electroplating.
Patent Document 2 discloses a method in which each of the collecting electrodes on the front side and the back side is formed of a plurality of layers including a first electrode electroconductive layer having a high light reflectance and a second electrode electroconductive layer having a low electric resistance. Patent Document 2 describes that collecting electrodes on the front side and the back side can be a plating method, and that when the collecting electrodes on the front side and the back side are made of the same material, these collecting electrodes can be formed simultaneously in the same step, so that the process can be simplified.
Patent Document 3 discloses a method in which an insulating film composed of SiO2 is formed on a transparent electrode layer, an insulating layer is then patterned using a resist, and a metal layer is formed in the opening by electroplating.